(1) Field of the Invention
This invention concerns an automatic on-off valve for use with a pneumatic micrometer adapted to economize the consumption of pressurized air during a not-measuring state of the micrometer.
(2) Disclosure of the Prior Art
Energy-saving measures have been taken in recent years for all of the technical fields in the industry. As for a pneumatic micrometer, for instance, pressurized air wasted in a state where no actual measurement is taken place for an object to be measured usually amount to about 50 Nl/min, which is 2-3 times as great as the air consumed in a state where measurement is actually taking place. Accordingly, various counter measures have been proposed for economizing the wasteful consumption of the pressurized air during the not-measuring state. As an example, a shut-off valve mounted on the measuring head is employed, in which the passage for flow of the pressurized air is opened during the measuring state to discharge the air for measurement and closed during the not-measuring state to interrupt the discharge of the air. Although the disposition of such a shut-off valve enables one to economize the pressurized air, it is not quite satisfactory in view of operativeness and reduced the working efficiency remarkably upon measurement due to the increase in the weight of the measuring head resulted from the attachment of the shut-off valve.
In order to overcome the foregoing problems, it may be effective to insert an automatic on-off valve between a main body of a pneumatic micrometer and its measuring head for automatically controlling the flow of pressurized air. As an example of an automatic on-off valve to attain such purpose, it can be so designed as to form two passages therein, one of which is a main flow passage to be opened and closed by a valve member to be automatically turned on or off by back pressure difference in the measuring head between the measuring state and the not-measuring state. The other passage is a sub-flow passage which is always put slightly open by means of a variable restrictor. However, the use of such an automatic on-off valve adapted as above would tend to worsen the measuring accuracy due to the error resulting from the disposition of the valve which introduces a throttling function into the measuring system.